The present invention relates generally to radio frequency (RF) power amplifiers, more specifically, to power sensing for RF power amplifiers.
Radio frequency transmission of an electrical signal occurs in a broad frequency spectrum from several megahertz (MHz) to tens of gigahertz (GHz). Common RF transmission systems include an antenna that transmits and receives RF signals and a low noise amplifier that amplifies an input RF signal from the antenna and a power amplifier to generate an amplified signal to be delivered to the antenna. The power of the output signals from the power amplifiers are required to be controlled within stringent specifications as well as regulatory standards, to assure the quality of the RF transmission signals. Moreover, many portable wireless systems are required to increase or reduce the transmitted power depending upon signal strength, transmission range, the types of digital signal modulation such as Quadrature Phase Shift Keying (QPSK) and Orthogonal Frequency Division Multiplexing (OFDM), as well as surrounding interfering signals. These requirements can be met by a power sensing circuit that samples the output power of the power amplifier and outputs a power sensing signal for power control. However, variations in power sensing signals due to temperature and DC bias are also passed on to the power output through the control loop. Variations in power sensing signals can significantly affect the qualities of the output RF signals. A need therefore exists for accurate and reliable techniques for power sensing for RF power amplifiers with good temperature and DC bias compensations.
The invention system generally includes a power sensing circuit for sensing radio frequency signals, comprising:
a) a first transistor to perform as a detector diode, including
i) a first base to receive a first radio frequency input signal output, a second DC bias signal from a regulated DC source coupled through a resistor, and a third power-sensing signal; and
ii) a first collector connected to the first base;
b) a second transistor to amplify the DC component of the RF signal from the first base, including
i) a second base connected to the first base through a low-pass filter; and
ii) a second collector to output the power-sensing signal to be coupled to the regulated DC source through a resistor, said power-sensing signal being substantially proportional to the strength of the first radio frequency input signal; and
c) an output port coupled to the second collector through a low-pass filter, to output the power-sensing signal.
In one aspect, the present invention provides a power sensing circuit for detecting power of a power amplifier. The power sensing circuit includes a detector diode using a transistor and a DC amplifier using a second transistor. The second transistor acts as a current mirror circuit regarding the DC current component of the first transistor and compensates variations in the power sensing circuit. The power sensing signal is provided in a single output terminal.
In another aspect, the present invention provides a circuit design that is simple and easy to implement using Heterojunctioh Bipolar Transistors (HBT) materials such as InGaP/Ga As which improves reliability relative to prior art.
An advantage of the present invention is that the temperature variation of the power sensing circuit is properly compensated to provide accurate power sensing at a wide temperature range.
Another advantage of the present invention is that the invention power sensing circuit directly senses the final output RF signal and can thus inclusively detect variations in the whole power amplifying circuit.
Yet another advantage of the present invention is that the invention power sensing circuit is simpler and easier to implement compared to prior art systems.
The details of one or more embodiments are set forth in the accompanying drawing and in the description below. Other features, objects, and advantages of the invention will become apparent from the description and drawings, and from the claims.